The present invention relates generally to explosive equipment for use in wells, and more particularly relates to improved detonation systems for use with such explosive equipment, such as, for example, well perforating equipment.
As is well known, down hole explosive devices utilize a detonator to selectively initiate detonation of one or more explosive devices, such as, for example, shaped charges in a perforating gun. In the case of a perforating gun, the perforating gun, including the detonator, is assembled with a set of shaped charges at the earth's surface. Such an assembled perforating gun, however, is vulnerable to accidental detonation through exposure to mechanical shock, spark or electrical impulse. Premature detonation is extremely dangerous, presenting a risk not only of property damage, but also of injury or death to the personnel at or near the rig floor.
The risk of accidental detonation can be especially significant in offshore environments. When a drilling rig has been placed on location and a well has been drilled through a body of water into formations below the body of water, it is necessary to continuously operate electronic equipment at the drilling rig. For instance, radio transmitters typically operate continuously to provide markers for navigational purposes and the like. Typically, there are many transmitters that operate in or on drilling rigs or platforms located in bodies of water. These transmitters each potentially represent EMF sources and present a risk of detonation of explosive devices through induced voltages.
Safety precautions in the past have involved shutting down most electrically powered equipment in the area of the rig floor. This has involved switching off radio transmitters, welding machines and lighting systems. In part, this has been to prevent sparks, electrical charges and magnetic fields which might detonate the explosive charges. Such extraordinary precautions not only require extreme communication and effort to achieve; but are also prone to human or mechanical error which can then again create a dangerous situation at the well site.
Accordingly, the present invention provides a novel detonating system for an explosive device, providing redundant safety mechanisms to avoid the explosive device being susceptible to detonation at the earth's surface. The invention further provides a detonator in a system which is substantially immune to induced voltages from EMF sources.